This invention relates to computer peripheral devices (e.g. disk drives, printers, etc.) and, more particularly, to an improved power supply for a computer peripheral device.
Most computer peripheral devices include a controllable element, control means coupled to the controllable element and operative in response to a power supply voltage of a predetermined level for controlling the controllable element, and power supply means coupled to the control means for supplying the power supply voltage to the control means. For example, a disk drive includes a movable carriage assembly to which one or more electromagnetic heads are affixed. The heads are then positionable over a desired track on a rotating magnetic recording disk by controlling the position of the carriage assembly. Positioning control is accomplished by a suitable servo control system. A power supply supplies the requisite d-c voltage or voltages to render the servo control system operative.
Power supplies commonly used nowadays in computer peripheral devices are characterized by a transmission line coupled to a source of a-c voltage, generally at a frequency of 50Hz or 60Hz, for supplying such a-c voltage to a rectifier circuit, usually a full-wave rectifier. The rectifier then generates a d-c voltage which, in the case of full-wave rectification, has a ripple frequency equal to twice the frequency of the a-c source, i.e. 100Hz or 120Hz. The output of the rectifier is then fed through an appropriate filter circuit to smooth out the ripple.
These power supplies suffer from a number of disadvantages. First, the relatively low ripple frequency (e.g. 50Hz or 60Hz in the case of half-wave rectification and 100Hz or 120Hz in the case of full-wave rectification) requires a relatively large and expensive filter capacitor. Second, the power supply is subject to electrical noise and signal transients in the a-c signal transmitted over the transmission line from the a-c voltage source to the rectifier circuit. Third, should the a-c source voltage be terminated or reduced in amplitude for brief instants of time, such as during so-called "brown-outs" or "black-outs", the d-c voltage output of the supply will likewise terminate or be reduced in amplitude, as the case may be. Fourth, these power supplies as a whole are relatively costly and large in size, thereby adding to the cost and size of the peripheral devices in which they may be included. Fifth, these known power supplies are relatively inefficient.
It would be desirable, therefore, to provide a power supply for a computer peripheral device which is substantially free of the above-mentioned disadvantages.